A laser sintering method of manufacturing a three-dimensional object by selectively solidifying of layers of a plastic powder material at locations corresponding to the cross-section of the object in the respective layer by impact of electromagnetic radiation, and a laser sintering device for manufacturing a three-dimensional object by selectively solidifying layers of a powdery material at locations corresponding to the cross-section of the object in the respective layer by impact of electromagnetic radiation, respectively, are known from DE 101 05 504 A1, for instance. In the method, in particular a plastic powder such as polyamide is used. Herein, polyamide 12 having a melting point of 185-189° C., an enthalpy of fusion of 112±17 kJ/mol and a solidification temperature of 138-143° C. is very suitable, as it is described in EP-0 911 142. The powder has an average grit size of 50-150 μm.
In the known method, a built-up process uses a certain amount of waste powder, that is, a powder remaining as non-sintered powder of one or several previous built-up processes.
Due to the stay in the process chamber during manufacturing of the three-dimensional object, the non-solidified powder is thermically and/or thermooxidatively damaged so that it has other material properties and also other processing parameters than fresh powder. Therefore, it can be mixed up with fresh powder only in a certain percentage, without compromising the built-up process and the building quality. The so-called fresh-up rate is the ratio between fresh powder and waste powder of the powder to be used in the built-up process. It should be as low as possible, since the costs for the fresh powder can be saved.
In DE 101 05 504 A1, a pre-treatment of the waste powder or of a mixture of waste powder and fresh powder before solidifying by liquefaction is proposed, so as to reduce the effects of aging damages and to enable admixing more waste powder. However, the pre-treatment by liquefaction does not remove all aging damages of the powder. In particular, a high ratio of waste powder causes unsatisfying surface properties of outer walls of the object by so-called pockmarks, which are also termed as “sink marks” or “orange peel”.
From WO 2005/097475 and DE 10 2004 047876 A1, laser sintering methods and laser sintering devices are known, which reduce the problem of pockmarks by using a determined material having increased stability in the laser sintering process and, thus, less aging damages, as it is used as waste powder. For instance, the powder according to DE 10 2004 047876 A1 is characterized in that it comprises a mixture of diamide- and diamine-controlled polyamide and/or co-polyamide. However, the user is forced to use this specific powder, which has in turn other properties than the previously used habitual powder and probably does not fulfil all requirements.
From DE 10 2006 023 484.7, it is further known that the problem of pockmarks is removed by mechanically compressing the powder building material during application of a layer. This requires a specific dispenser. From US 2004/0138344 A1, it is known to increase the melting point and the enthalpy of fusion of polyamide by contacting the polyamide with water or water vapour. Thereby, some polyamide can be made suitable for laser sintering.
It is the object of the invention to provide a method and a device of manufacturing a three-dimensional object and, in particular, a laser sintering method and a laser sintering device, which can reduce the fresh-up rate and, therefore, the costs of the method, and which can enhance the environmental compatibility as well.